Mixing of Longitudinal and Transverse Dynamics in Liquid Water

Sampoli, M.; Ruocco, G.; Sette, F.

doi:10.1103/physrevlett.79.1678

Cited by 155 publications

(178 citation statements)

References 21 publications

Supporting

Mentioning

148

Contrasting

Order By: Relevance

“…25 However, it should be noted that the density fluctuation modes loose their symmetry as the wave vector is increased, so that the longitudinal and transverse terms have not a well defined significance. Accordingly, the visibility of a transverse excitation in the intrinsically longitudinal density fluctuation spectra of a disordered system can be justified by the mixing phenomenon, 26 or, in other words, at high frequency the transverse dynamics acquire a longitudinal component, observable in the neutron and x-ray scattering experiments. The incoherent scattering experiment does not provide a direct insight on the behavior of glassy glucose apart form the presence of the translational modes up to more than 20 meV, as it is also seen in the coherent scattering experiment.…”

Section: Methodsmentioning

confidence: 99%

Neutron scattering investigation of high-frequency dynamics in glassy glucose

et al. 2012

View full text Add to dashboard Cite

The vibrational dynamics of vitreous glucose has been investigated by means of inelastic neutron scattering experiments, exploiting the coherent scattering cross section of deuterium in a fully deuterated sample and the high incoherent scattering cross section of hydrogen in a hydrogenated sample. The first part of the experiment allowed a rather detailed investigation of the collective dynamics in the THz range. The second part of the experiment was used to derive some information on the vibrational density of states of the system. The experiment confirms the presence of a propagating vibrational mode which is the natural extension at THz frequencies of the lower frequencies longitudinal sound mode. In addition, a second mode is also observed at a lower and almost constant frequency, showing an increasing intensity on reducing the wavelength. By comparing the dispersion relations of these collective modes to the experimental density of states, a possible relation between the low frequency mode and the well known excess of low frequency modes, that is, the boson peak, is identified.

show abstract

Section: Methodsmentioning

confidence: 99%

Neutron scattering investigation of high-frequency dynamics in glassy glucose

et al. 2012

View full text Add to dashboard Cite

show abstract

“…This second excitation has a (almost) Q-independent energy, and becomes visible only at Q larger than ≈4 nm −1 . This second feature, observed in the S(Q, ω) of ambient condition liquid water by INS [6,8,9,10] and IXS [12,13,16], has been attributed to transverse-like dynamics on the basis of a MD study [18] where the comparison between longitudinal and transverse current spectra was performed. The existence of the second feature and its transverse origin can be explained within the same viscoelastic framework which has been successfully used to describe the longitudinal dynamics.…”

Section: Introductionmentioning

confidence: 99%

High-frequency longitudinal and transverse dynamics in water

et al. 2005

Self Cite

View full text Add to dashboard Cite

High-resolution, inelastic x-ray scattering measurements of the dynamic structure factor S(Q, ω) of liquid water have been performed for wave vectors Q between 4 and 30 nm −1 in distinctly different thermodynamic conditions (T= 263 -420 K ; at, or close to, ambient pressure and at P = 2 kbar). In agreement with previous inelastic x-ray and neutron studies, the presence of two inelastic contributions (one dispersing with Q and the other almost non-dispersive) is confirmed.The study of their temperature-and Q-dependence provides strong support for a dynamics of liquid water controlled by the structural relaxation process. A viscoelastic analysis of the Q-dispersing mode, associated with the longitudinal dynamics, reveals that the sound velocity undergoes the complete transition from the adiabatic sound velocity (c 0 ) (viscous limit) to the infinite frequency sound velocity (c ∞ ) (elastic limit). On decreasing Q, as the transition regime is approached from the elastic side, we observe a decrease of the intensity of the second, weakly dispersing feature, which completely disappears when the viscous regime is reached. These findings unambiguously identify the second excitation to be a signature of the transverse dynamics with a longitudinal symmetry component, which becomes visible in the S(Q, ω) as soon as the purely viscous regime is left.

show abstract

“…Anyway, sound propagates through glasses and longitudinal and transverse phonons are found to be still well defined at relatively large wave-vectors (up to 5 nm −1 ) with a linear relationship between frequency (ω) and exchanged wavevector (q) [16,17]. Beyond this limiting q value, the effect of the topological disorder of the glassy systems causes (i) a mixing of the polarisation of the acoustic modes, which is observed for different glass forming systems both in experimental [16,18,19] and in molecular dynamic simulations (MDS) data [17,20] and (ii) a possible presence of positive dispersion in the longitudinal acoustic branch [16], as theoretically predicted [21] and found in MDS [17]. Since below such q values, v-SiO 2 exhibits a substantially constant sound velocity, so the dependence of the sound attenuation on ω can be safely investigated by changing the wavevector q.…”

mentioning

confidence: 99%

Sound attenuation in a unexplored frequency region: Brillouin ultraviolet light scattering measurements inv−SiO2

et al. 2005

Self Cite

View full text Add to dashboard Cite

We report Ultraviolet Brillouin light scattering experimental data on v-SiO2 in an unexplored frequency region, performed with a newly available spectrometer up to exchanged wavevector q values of 0.075 nm −1 , as a function of temperature. The measured attenuation scales on visible data following a q 2 behavior and is temperature-dependent. Such temperature dependence is found in a good agreement with that measured at lower q, suggesting that its origin is mainly due to a dynamic attenuation mechanism. The comparison between the present data with those obtained by Inelastic X-ray Scattering suggests the existence of a cross-over to a different attenuation regimes. Our present understanding of the sound attenuation mechanisms in vitreous systems is poor compared to that of crystalline materials although this topic has attracted the interest of several researchers from both experimental and theoretical points of view [1]. In particular, the nature of vibrational dynamics of disordered systems, as derived from the study of the "low-frequency" excitations (in the hypersonic range), has been a highly debated subject in the last years [2,3,4,5,6]. Vitreous silica (v-SiO 2 , or amorphous quartz) has been extensively studied as prototype of a strong glass. Nevertheless, the experimental results reported in literature had conflicting and controversial interpretations [7,8,9,10,11]. To achieve an overall characterization of this particular system is crucial to understand the vibrational dynamics of the vitreous state. It is well known that a plane wave excitation can propagate freely in a disordered structure only when the wavelength is much greater than the scale spanned by microscopic inhomogeneities. As the wavelength shortens the wave is attenuated, distorted, and scattered with increasing magnitude. As a matter of fact, the waves can even become over-damped when the wavelength approaches the interparticle spacing and the excitations become more directly affected by the microscopic disorder characteristic of the glass structure. The question about the nature of excitations far from the long wavelength limit, is unlikely to have a single answer [12,13,14]. Indeed different mechanisms have been suggested in order to explain the attenuation of an acoustic plane wave excitation namely: attenuation induced by topological disorder, thermally activated processes, anharmonic effects, two-level systems (TLS) processes [15]. In general, anharmonic effects are particularly relevant at relatively high temperatures while the importance of the two-level systems is confined at very low temperatures (T < 5 ÷ 10 K). In the intermediate range 10 K < T ≪ T g the TLS effects are not important and disordered induced mechanisms, thermally activated processes and anharmonic effects play the most important role in acoustic attenuation. Anyway, sound propagates through glasses and longitudinal and transverse phonons are found to be still well defined at relatively large wave-vectors (up to 5 nm −1 ) with a linear relationship between frequen...

show abstract

Mixing of Longitudinal and Transverse Dynamics in Liquid Water

Cited by 155 publications

References 21 publications

Neutron scattering investigation of high-frequency dynamics in glassy glucose

Neutron scattering investigation of high-frequency dynamics in glassy glucose

High-frequency longitudinal and transverse dynamics in water

Sound attenuation in a unexplored frequency region: Brillouin ultraviolet light scattering measurements inv−SiO2

Contact Info

Product

Resources

About